More sheets are consumed as the amount of various kinds of information increases. On the other hand, sheets are recycled in order to save the resource of sheets. For example, in recycling of sheets, used sheets having image information thereon made of toners and the like are processed using a large amount of bleaching agent and water, and thus recycled sheets are manufactured. Therefore, the recycling of sheets brings about the increase in the cost of recycles sheets, which diminishes the cost effectiveness and may incur new environment pollution resulting from treatment of waste water used during regeneration of used sheets.
In view of the above circumstances, a technique has been recently developed to greatly reduce the amount of actual use of sheets. According to this technique, erasable image forming material made of resin, pigment, color fixing agent, erasing agent, and the like is used to form an image on a sheet. This formed image is decolorized from the sheet by an image decolorizing device, and a white sheet is obtained. This white sheet from which the image has been decolorized is reused multiple times. According to this technique, the overall cost relating to reuse of sheets can be reduced.
For example, an image forming apparatus having an image decolorizing function for decolorizing color of image forming material by heating a sheet and capable of preventing misuse of a reused sheet has been known.
The above-described image forming apparatus has not only the image forming function but also the decolorizing function for decolorizing an image by heat. In addition, a detecting sensor is used to detect whether a mark indicating reusable sheet is attached to a sheet or not. Therefore, even when a user stacks both of reusable sheets and nonreusable sheets on a sheet feed tray in a mixed manner, the image forming apparatus can distinguish the reusable sheets. That is, the image forming apparatus performs image decolorizing processing on sheets attached with the mark indicating reusable sheet, and does not perform image decolorizing processing on sheets without the mark.
However, in the above-described image forming apparatus having the decolorizing device, if the decolorizing device is feeding sheets placed at an insertion opening in order to perform decolorizing processing on previously-inserted sheets when the user tries to perform decolorizing processing, the user is unable to insert sheets even though the user tries to feed sheets to perform new decolorizing processing on the sheets. In other words, in the case where the image forming apparatus has only one stacker for stacking sheets which are to be subjected to decolorizing processing, the uppermost sheet of stacked sheets is fed into the image forming apparatus while decolorizing processing is performed. Therefore, during the feeding operation, the user is unable to place sheets on the stackers. In addition, in the case where the placed sheets are fed in order from a feeding opening, there is a problem in that only the upper portion of the placed sheets are always reused repeatedly, resulting in low recycling efficiency. Still more, since sheets processed by the decolorizing device are already-used sheets, the sheets could be curled. When the sheets are curled, there is a possibility that the sheets are jammed during feeding operation and the processing cannot be carried out smoothly.